A hybrid vehicle indicates a vehicle driven by an efficient combination of at least two different kinds of power sources. Hybrid vehicles often indicate vehicles driven by an engine that generates a torque by combusting fuel and a motor that generates a torque by electric energy of a battery.
The hybrid vehicle may have various power transfer structures using the engine and the motor and some hybrid vehicles adopt one of a parallel type power transfer structure or a serial type power transfer structure.
Further, the hybrid vehicle may generate an optimal output torque depending on how to concurrently operate the engine and the motor while the hybrid vehicle is driven by two power sources including the engine and the motor.
A typical powertrain arrangement of the hybrid vehicle is a type in which an engine clutch is installed between the engine and the motor and has a structure in which an engine, a starting generator for engine starting and power generation, an engine clutch interposed between the engine and the motor, a motor (driving motor), and a transmission are sequentially arranged. Further, the motor and the starting generator are connected to the battery through an inverter to be chargeable and dischargeable.
Meanwhile, in a hybrid vehicle in which an automatic transmission is mounted, a shift time may be shortened by an optimal slip control of a clutch and a brake using a fluid (transmission oil) during a shift and a sense of difference, or a large shift, occurring at the time of the shifting is minimized.
Further, to reduce a shock generated when the clutch within the transmission during the shift is engaged or disengaged, a torque intervention control is performed to instantaneously reduce a transmission input torque.
In a typical automatic transmission hybrid vehicle, a torque control target for reducing the transmission input torque when the torque intervention is requested is the engine and the motor and to reduce the transmission input torque, a control to reduce an engine torque itself or reduce the transmission input torque while the engine operation torque is transferred to the motor to perform a power generation operation of the motor (absorb an engine output by charging the battery) has been performed.
FIG. 1 is a diagram illustrating a control instruction to perform a torque intervention according to the related art. As illustrated in FIG. 1, if the intervention is requested, a torque reduction amount is calculated and a motor charging available amount is calculated to output a motor torque and an engine torque.
In more detail, when a maximum torque (here, the torque means a torque absolute value and the torque upon the power generation is an actual negative torque) of the motor for a power generation operation or a maximum torque (negative torque, maximum generation possible torque) of the motor considering a state of charge (SOC) of the battery is equal to or more than ‘abs ((engine target RPM−engine current RPM)×engine inertia)+abs (engine operation torque−intervention requested torque)’, the engine is controlled by the engine operation torque of an instruction value before the intervention without reducing the torque Here, ‘abs ( )’ represents an absolute value.
In this case, the motor for the power generation operation performs the torque control based on the value of the ‘abs ((engine target RPM−engine current RPM)×engine inertia)+abs (engine operation torque intervention requested torque)’.
If the maximum torque of the motor for the power generation operation, the maximum torque of the motor considering the state of charge (SOC) of the battery, or the like is smaller than the ‘abs ((engine target RPM−engine current RPM)×engine inertia)+abs (engine operation torque−intervention requested torque)’, the intervention requested torque control for reducing the output torque depending on an intervention yoke value by a control of ignition timing is performed on the engine. In this case, a zero torque control is performed on the motor.
However, the existing shift control scheme is a scheme of delaying the ignition timing while supplying and consuming fuel during the engine torque control for the torque intervention and reduces the engine torque to reduce engine efficiency (causing a reduction in fuel efficiency).
In addition, a hybrid vehicle having two motors has been developed recently. In the hybrid vehicle, the strategies of the torque intervention control and the driving source control that may minimize an energy loss and maximize drivability upon the switching of a series-parallel mode or the parallel shift control have not yet been proposed.